It was Archimedes who first realised, in his “eureka” moment, that a body that is immersed completely in water will displace a volume of water equal to the volume of the body and that the apparent weight of the body, when immersed, will be reduced by the weight of water displaced.

As with any engineering product, precision is necessary in defining the geometry of a ship. Again, in common with most disciplines, an internationally recognised terminology has grown up over the years to aid this definition.

So far, consideration has been given only to a ship when in equilibrium or moving slowly from one position of equilibrium to another. Now consider what happens when a ship is subject to a small heeling moment.

A table of offsets, although accurately defining the hull shape, does not provide an immediate feel of the main characteristics of that shape. There are some “coefficients” which can be obtained for the underwater hull which provide clues as to its general nature and its likely behaviour.